This invention relates to a heat exchanger for cooling exhaust gas of an internal-combustion engine having a plurality of ducts for guiding the exhaust gas which are provided with lugs arranged in pairs diagonally to the flow direction and projecting from at least one wall of the ducts, and a liquid cooling medium flowing on the outside around the ducts. This invention also relates to a method of manufacturing such a heat exchanger.
In the case of a known heat exchanger of the initially mentioned type, the ducts are formed of disk-shaped heat exchange elements between which one turbulence insert respectively is arranged which has lugs which are arranged in pairs and extend diagonally to the flow direction. This heat exchanger known from German Patent Document DE-U 94 06 197.1 fulfills its task satisfactorily. However, considerable expenditures are required to implement heat exchangers of different sizes for different vehicles because the individual elements must then be manufactured with accurate measurements in the different sizes.
It is an object of the invention to provide a heat exchanger of the initially mentioned type which can be manufactured in different sizes, in which case no excessively high variations in dimension must be maintained for the individual structural elements.
This and other objects have been achieved according to the present invention by providing a bundle of rectangular tubes as ducts for the exhaust gas whose ends are welded into latticed tube bottoms, wherein the bundle of rectangular tubes is surrounded by a sheet metal jacket which follows the contour of the bundle, is provided with a cooling medium inlet and a cooling medium outlet and is welded to the tube bottoms, and wherein the ends of the sheet metal jacket are provided with welded-on flange plates which are open with respect to the bundle of rectangular tubes by way of a central opening and which are provided with fastening devices for attachment with pipe sections of an exhaust gas pipe.
This and other objects have been achieved according to the present invention by providing a heat exchanger for cooling exhaust gas of an internal-combustion engine, comprising a plurality of tubes for guiding exhaust gas; first and second latticed tube bottoms, each tube bottom defining a plurality of openings corresponding to an outer periphery of respective of the tubes, first and second axial ends of each of the tubes being arranged in respective of the openings in the first and second tube bottoms such that the tube bottoms support the tubes substantially parallel to one another and spaced-apart from one another in a bundle; a sheet metal jacket concentrically surrounding the bundle and attached to the tube bottoms, the sheet metal jacket and the tube bottoms defining a chamber, the sheet metal jacket being provided with a coolant inlet and a coolant outlet to allow a liquid coolant to enter the chamber, flow around an exterior surface of the tubes in the chamber, and exit the chamber; and flange plates attached to ends of the sheet metal jacket and configured for attachment to an exhaust pipe, each the flange plate defining an opening which communicates an interior of the tubes with an interior of the exhaust pipe.
This and other objects have been achieved according to the present invention by providing a method of manufacturing a heat exchanger for cooling exhaust gas of an internal-combustion engine, the method comprising the steps of: providing a plurality of rectangular tubes for guiding exhaust gas; attaching a plurality of lugs to the rectangular tubes diagonally to a flow direction of the exhaust gas, the lugs being arranged in pairs; attaching ends of the rectangular tubes to the latticed tube bottoms such that the rectangular tubes form a bundle; attaching a sheet metal jacket to the tube bottoms and around the bundle; providing the sheet metal jacket with a coolant inlet and a coolant outlet to allow a liquid coolant to flow around the rectangular tubes in the sheet metal jacket; and attaching flange plates to ends of the sheet metal jacket, the flange plates being configured for attachment to an exhaust pipe, each flange plate defining a central opening which communicates the rectangular tubes with the exhaust pipe.
The heat exchanger according to the present invention essentially comprises sheet metal components which can be manufactured in a simple manner, for example by welding. Welding is preferably carried out by laser welding or micro TIG welding. The latticed tube bottoms, which may be stamped out of a steel plate, have openings corresponding to the number and arrangement of the rectangular tubes. In certain preferred embodiments, the thickness of the steel plate is approximately 1 mm to 3 mm. The distances between the rectangular tubes, and correspondingly the web width of the tube bottoms, vary according to the desired mass flow rate of the coolant. In certain preferred embodiments, these distances are approximately 1 mm to 3 mm. The outer contour of the tube bottoms depends upon the number and the arrangement of the flat tubes. The sheet metal jacket also may be made in a simple manner from a steel plate which has a sheet metal thickness which is similar to the tube bottoms. The sheet metal jacket can be edged in a simple manner in steps corresponding to the contour of the tube bottoms. The flange plates, which are provided with fastening devices, permit in a simple manner an arrangement of the heat exchanger between two pipe sections of an exhaust pipe, for example, in a manner similar to the arrangement of a catalyst.
In a further development of the invention, the rectangular tubes are each formed by two tube shells which are welded together. The lugs existing in pairs can be fastened directly to the rectangular tube or can be a component of this rectangular tube. However, they can also be a component of inserts arranged in the rectangular tubes.
In a further development of the invention, the flange plates are provided with threaded sleeves in mutually essentially diametrically opposite areas. As a result, the flange plates may be screwed to mating flanges of a pipe section in an exhaust pipe in a simple manner.
In an advantageous further development of the invention, the sheet metal jacket is provided with a cooling medium inlet in the proximity of the flange plate which is in the front in the flow direction of the exhaust gas and is provided with a cooling medium outlet in the proximity of the rear flange plate. As a result, the cooling medium is guided through the heat exchanger in a co-current flow with the exhaust gas. Thus, the risk of a vapor formation on the inlet side of the exhaust gas is reduced because here the cooling medium has the relatively lowest temperature.
In a further development of the invention, the cooling medium inlet and the cooling medium outlet are arranged on opposite sides of the sheet metal jacket. Because of this arrangement, the flow paths of the individual current routes for the cooling medium around the rectangular tubes essentially have the same length ensuring a uniform flow around these rectangular tubes.
In a further development of the invention, the sheet metal jacket is composed of two preformed sheet metal shells which adjoin the tube bottoms by means of joint connections. After being welded together, the two sheet metal shells form a stiff and pressure-resistant housing. The joint connections provide the advantage that the elements to be welded together have a certain cohesion already before being welded, so that the welding operation can be carried out in a relatively simple manner.
For the same purpose, in a further development of the invention the flange plates adjoin the sheet metal jacket by means of joint connections. Furthermore, it is provided for the same purpose that the threaded sleeves adjoin the flange plates by means of a joint connection. As a result, the welding operation can be carried out in a relatively simple manner.
These and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.